Solar cell and method of manufacturing the same

ABSTRACT

A solar cell and a method of manufacturing the same are provided. The solar cell includes: i) a first conductive layer; ii) a plurality of nano structures that are positioned on the first conductive layer and that are extended to cross a surface of the first conductive layer and that are separated from each other; iii) a resin layer that is positioned on the first conductive layer and that is filled at space between the plurality of nano structures; iv) at least one semiconductor layer that is positioned on the resin layer and that covers the plurality of nano structures; and v) a second conductive layer that covers the semiconductor layer and that has a light transmittance lower than that of the first conductive layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2010-0051094 and 10-2011-0051965 filed in the KoreanIntellectual Property Office on May 31, 2010 and May 31, 2011, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a solar cell and a method ofmanufacturing the same. More particularly, the present invention relatesto a solar cell and a method of manufacturing the same that have animproved light absorption efficiency and photoelectric conversionefficiency.

(b) Description of the Related Art

Nowadays, due to resource exhaustion and increase of a resource price,research and development of clean energy has been actively performed.Clean energy includes, for example, sun energy, wind energy, and tidalenergy. Particularly, in order to efficiently use sun energy, researchand development of a solar cell has been continuously performed.

A solar cell is an apparatus that converts light energy of sun toelectrical energy. When sun light is applied to the solar cell,electrons and holes are generated at the inside of the solar cell. Thegenerated electrons and holes are moved to a P electrode and an Nelectrode that are included in the solar cell, a potential differenceoccurs between the P electrode and the N electrode and thus a currentflows.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a solar cellhaving advantages of being capable of producing using a simple processand excellent photoelectric conversion efficiency and light absorptionefficiency. The present invention has been made in an effort to furtherprovide a method of manufacturing the solar cell.

An exemplary embodiment of the present invention provides a solar cellincluding: i) a first conductive layer; ii) a plurality of nanostructures that are positioned on the first conductive layer and thatare extended to cross a surface of the first conductive layer and thatare separated from each other; iii) a resin layer that is positioned onthe first conductive layer and that is filled at space between theplurality of nano structures; iv) at least one semiconductor layer thatis positioned on the resin layer and that covers the plurality of nanostructures; and v) a second conductive layer that covers thesemiconductor layer and that has a light transmittance lower than thatof the first conductive layer.

The solar cell may further include a dielectric layer that is positionedon a surface of the plurality of nano structures and that contacts withthe resin layer. The second conductive layer may have a thickness of 20μm to 100 μm. The solar cell may further include at least one electrontransfer body that is positioned on the first conductive layer and thatcontacts with a lower end portion of the plurality of nano structures.The second conductive layer and the electron transfer body may includethe same metal. The metal may be at least one element that is selectedfrom a group consisting of aluminum (Al), silver (Ag), nickel (Ni), gold(Au), and platinum (Pt). The at least one electron transfer body mayinclude a plurality of electron transfer bodies, and the plurality ofelectron transfer bodies may be separated from each other. The electrontransfer body may have an average diameter larger than that of theplurality of nano structures.

The electron transfer body may cover the first conductive layer, and theelectron transfer body may include a p+ type semiconductor material oran n+ type semiconductor material. The at least one semiconductor layermay include a plurality of semiconductor layers, and a semiconductorlayer contacting with the electron transfer body of the plurality ofsemiconductor layers may include an intrinsic material.

The at least one semiconductor layer may include a plurality ofsemiconductor layers, and at least one semiconductor layer of theplurality of semiconductor layers may include i) a plurality of firstsemiconductor portions that are positioned on the plurality of firstnano structures; and ii) a second semiconductor portion that isconnected to the first semiconductor portion to be integrally formedwith the first semiconductor portion and that is positioned on the resinlayer. A width between upper end portions of the plurality of firstsemiconductor portions may be 100 nm to 2 μm.

The solar cell may further include a cover layer that covers the secondconductive layer and that contacts with a side surface of the resinlayer. The solar cell may further include a contact electrode that ispositioned within the cover layer and that electrically connects thesecond conductive layer to the outside by contacting with the secondconductive layer.

The plurality of nano structures may include a semiconductor material.The first conductive layer may have a thickness of 30 nm to 300 nm. Thedielectric layer may include at least one material that is selected froma group consisting of aluminum oxide (Al₂O₃), silicon nitride (SiN_(x)),silicon carbide (SiC), and silicon dioxide (SiO_(x)).

Another embodiment of the present invention provides a solar cellincluding: i) a first conductive layer; ii) a plurality of nanostructures that are positioned on the first conductive layer and thatare extended to cross a surface of the first conductive layer and thatare separated from each other; iii) a plurality of semiconductor layersthat cover the plurality of nano structures; and iv) a second conductivelayer that covers the plurality of semiconductor layers and that has alight transmittance higher than that of the first conductive layer. Atleast one semiconductor layer of the plurality of semiconductor layersincludes i) a plurality of first semiconductor portions that arepositioned on the plurality of nano structures; and ii) a secondsemiconductor portion that is connected to the plurality of firstsemiconductor portions to be integrally formed with the plurality offirst semiconductor portions and that is positioned on the firstconductive layer.

The second conductive layer may have a light transmittance lower by 90%to 99% than that of the first conductive layer in a visible ray area. Adiameter of the plurality of nano structures may reduce as being awayfrom a surface of the first conductive layer. The plurality of nanostructures may include i) a first nano structure that is applied to trapincident light; and ii) a second nano structure that is positionedtogether with the first nano structure and that is applied to convertincident light to power.

The solar cell may further include another semiconductor layer that ispositioned between the first conductive layer and the plurality of nanostructures. The other semiconductor layer may include an n+ typesemiconductor material or a p+ type semiconductor material. A lowersurface of the plurality of nano structures contacting with the othersemiconductor layer may be unevenly formed. The solar cell may furtherinclude an anti-reflection layer that is positioned under the firstconductive layer.

Yet another embodiment of the present invention provides a method ofmanufacturing of a solar cell, the method including: i) providing asubstrate and a plurality of nano structures that are positioned on thesubstrate and that are separated from each other; ii) providing a resinlayer that are positioned on the substrate and that fills space betweenthe plurality of nano structures; iii) partially exposing the pluralityof nano structures by etching an upper portion of the resin layer; iv)providing at least one semiconductor layer on the exposed plurality ofnano structures; v) providing a conductive layer on the semiconductorlayer; vi) providing a cover layer that covers the conductive layer;vii) separating the substrate; and viii) providing another conductivelayer having a light transmittance lower than that of the conductivelayer under the resin layer.

The method may further include providing a dielectric layer thatcontacts with the resin layer and that is positioned on a surface of theplurality of nano structures. The partially exposing of the plurality ofnano structures may include etching a dielectric layer contacting withan upper portion of the resin layer among the dielectric layer. Theproviding of a conductive layer may include performing electrolessplating of the conductive layer on the semiconductor layer. The methodmay further include: after the separating of the substrate, i) forming ahole that exposes a lower end portion of the plurality of nanostructures to the outside in the resin layer by etching the resin layer;and ii) providing an electron transfer body to the hole. The providingof an electron transfer body may include providing the electron transferbody by electroless plating.

The providing of a substrate and a plurality of nano structures mayinclude decreasing a diameter of the plurality of nano structures asbeing away from a surface of the substrate. The substrate and theplurality of nano structures may be integrally provided by electrolessetching. The plurality of nano structures may be additionally etched.

At providing of a cover layer, the cover layer may include a resin. Atthe providing of at least one semiconductor layer, the at least onesemiconductor layer may include a plurality of semiconductor layers, andthe plurality of semiconductor layers may be formed by ion doping. Themethod may further include providing, after the providing of aconductive layer, a contact electrode that electrically connects theconductive layer to the outside by contacting with the conductive layeron the conductive layer.

Yet another embodiment of the present invention provides a method ofmanufacturing a solar cell, the method including: i) providing asubstrate and a plurality of nano structures that are positioned on thesubstrate and that are separated from each other; ii) providing at leastone semiconductor layer on the plurality of nano structures; iii)providing a conductive layer on the semiconductor layer by electrolessplating; providing a cover layer that covers the conductive layer; iv)separating the substrate; and v) providing another conductive layerhaving a light transmittance lower than that of the conductive layerunder the plurality of nano structures.

The method may further include providing another semiconductor layerbetween the plurality of nano structures and the other conductive layer.At the providing of another semiconductor layer, the other semiconductorlayer may include a p+ type semiconductor material or an n+ typesemiconductor material. The method may further include providing ananti-reflection layer under the other conductive layer.

A solar cell having an excellent light absorption efficiency andphotoelectric conversion efficiency can be produced using a nanostructure, a dielectric layer, and a resin layer. Further, because asolar cell is produced by separating the substrate, the substrate can berecycled. A solar cell can be simply produced using an electrolessetching method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a solar cellaccording to a first exemplary embodiment of the present invention.

FIG. 2 is a schematic flowchart illustrating a method of manufacturingthe solar cell of FIG. 1.

FIGS. 3 to 12 are cross-sectional views sequentially illustrating amethod of manufacturing the solar cell of FIG. 1.

FIG. 13 is a schematic cross-sectional view illustrating a solar cellaccording to a second exemplary embodiment of the present invention.

FIG. 14 is a schematic flowchart illustrating a method of manufacturingthe solar cell of FIG. 13.

FIGS. 15 to 20 are cross-sectional views sequentially illustrating amethod of manufacturing the solar cell of FIG. 13.

FIG. 21 is a schematic cross-sectional view illustrating a solar cellaccording to a third exemplary embodiment of the present invention.

FIG. 22 is a schematic cross-sectional view illustrating a solar cellaccording to a fourth exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

When it is said that any part is positioned “on” another part, it meansthe part is directly on the other part or above the other part with atleast one intermediate part. In contrast, if any part is said to bepositioned “directly on” another part, it means that there is nointermediate part between the two parts.

Technical terms used here are to only describe a specific exemplaryembodiment and are not intended to limit the present invention. Singularforms used here include a plurality of forms unless phrases explicitlyrepresent an opposite meaning. A meaning of “comprising” used in aspecification embodies a specific characteristic, area, integer, step,operation, element and/or component and does not exclude presence oraddition of another specific characteristic, area, integer, step,operation, element, component and/or group.

Terms representing relative space of “low” and “upper” may be used formore easily describing a relationship to another portion of a portionshown in the drawings. Such terms are intended to include other meaningsor operations of a using apparatus together with a meaning that isintended in the drawings. For example, when an apparatus is inverted inthe drawings, any portion described as disposed at a “low” portion ofother portions is described as being disposed at an “upper” portion ofother portions. Therefore, an illustrative term of “low” includes entireupper and lower directions. An apparatus may rotate by 90° or anotherangle, and a term representing relative space is accordingly analyzed.

Although not differently defined, entire terms including a technicalterm and a scientific term used here have the same meaning as a meaningthat may be generally understood by a person of common skill in the art.It is additionally analyzed that terms defined in a generally useddictionary have a meaning corresponding to a related technology documentand presently disclosed contents and are not analyzed as an ideal orvery official meaning unless stated otherwise.

A term of “nano” using hereinafter means that a size of an object is anano unit. However, a nano unit may be analyzed to include a micro unit.

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art would realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention.

FIG. 1 is a schematic cross-sectional view illustrating a sectionstructure of a solar cell 100 according to a first exemplary embodimentof the present invention. The section structure of the solar cell 100 ofFIG. 1 only illustrates the present invention, and the present inventionis not limited thereto. Therefore, the section structure of the solarcell 100 may be changed to other forms.

As shown in FIG. 1, the solar cell 100 includes a first conductive layer10, a plurality of nano structures 20, a dielectric layer 22, a resinlayer 30, a plurality of semiconductor layers 40, and a secondconductive layer 50. In addition, the solar cell 100 may further includean electron transfer body 24, a cover layer 70, contact electrodes 60and 62, and a drawn-out wiring 80. Power that is generated by the lightin the solar cell 100 is used for driving a passive element P.Meanwhile, the solar cell 100 may further include other elements inaddition to elements that are shown in FIG. 1.

Because the first conductive layer 10 and the second conductive layer 50are connected to the contact electrodes 60 and 62 and the drawn-outwiring 80, respectively, power that is generated in the solar cell 100drives the passive element P. As indicated by an arrow of FIG. 1, lightis applied in a +z-axis direction through the first conductive layer 10.Therefore, the first conductive layer 10 is a transparent electrode andis transparently formed to transmit light using a material such asindium tin oxide (ITO) or zinc oxide that is doped with Al/Ga.

The second conductive layer 50 reflects again light to the semiconductorlayer 40, thereby maximizing generation of an electromotive force. Forthis purpose, the second conductive layer 50 is formed in an opaquelayer to well reflect and is made of a metal material. For example, thesecond conductive layer 50 may include aluminum (Al), silver (Ag),nickel (Ni), gold (Au), or platinum (Pt). When the semiconductor layer40 is made of an n+ type semiconductor material, aluminum (Al) or silver(Ag) that forms an ohmic contact is used as a material of the secondconductive layer 50. Further, when the semiconductor layer 40 is made ofa p+ type semiconductor material, nickel (Ni), gold (Au), or platinum(Pt) is used as a material of the second conductive layer 50. The secondconductive layer 50 has a light transmittance lower than that of thefirst conductive layer 10. Therefore, because light does not passthrough the second conductive layer 50 and is totally reflected, lightis converted to power by the plurality of nano structures 20 and thesemiconductor layer 40.

More specifically, in a visible ray area, a light transmittance of thesecond conductive layer 50 is lower by 90% to 99% than that of the firstconductive layer 10. By adjusting a light transmittance differencebetween the first conductive layer 10 and the second conductive layer 50to the above-described range, light loss in the solar cell 100 may beminimized. The second conductive layer 50 does not transmit light. Here,the second conductive layer 50 may be formed using an electrolessdeposition method or an electrolysis deposition method. The secondconductive layer 50 functions as a back reflector that well absorbs nearinfrared rays having a wavelength range of 1100 nm to 1600 nm.Therefore, the nano structure 20 can absorb light to the maximum due tothe second conductive layer 50. Consequently, while maximizing aquantity of light that passes through the first conductive layer 10within the above-described light transmittance range, reflectivity oflight by the second conductive layer 50 can be maximized.

As shown in FIG. 1, the plurality of nano structures 20 are separatelypositioned on the first conductive layer 10. The plurality of nanostructures 20 are extended in a direction crossing a surface 101 of asubstrate 10, i.e., in +z-axis direction. The nano structure 20 has acone shape. Although not shown in FIG. 1, the nano structure 20 may havea cylindrical shape. The nano structure 20 that is formed as monocrystalis made of an n-type material or a p-type material and absorbs light.

Because the semiconductor layer 40 is conformally formed with the nanostructure 20, the semiconductor layer 40 absorbs well light by a shortcarrier collection. Further, the plurality of nano structures 20 do notabsorb light as an n+ type or a p+ type and may be used as an electricalpassage of electrons or holes that are absorbed from the stackedsemiconductor layer 40. In this case, the plurality of nano structures20 function as an n+ selective emitter and quickly transfer electrons orholes that are absorbed by a single carrier collection by thesemiconductor layer 40 to an emitter, thereby preventing a recombinationthereof. Therefore, because a large amount of electrons and holes aregenerated, generation of an electromotive force may be maximized usingthe generated large amount of electrons and holes. Further, the nanostructures 20 and the semiconductor layer 40 maximizes light absorptionefficiency by trapping light through a stacked structure thereof.Because the plurality of nano structures 20 have a cone shape, adiameter of the plurality of nano structures 20 decreases as being awayfrom a surface of the first conductive layer 10.

In general, solar cells to which light is applied much exist at an upperend portion of a cone of shapes of a nano structure. However, in anexemplary embodiment of the present invention, by producing the solarcell 100 with an opposite method, an light absorption efficiency by theplurality of nano structures 20 can be maximized. That is, incidentlight is well absorbed to the inside of the solar cell 300 by multiplereflection and scattering effects. Further, electrons or holes that aregenerated in the nano structures 233 perform carrier collection throughthe second conductive layer 75 by tunneling an oxide film 33. Asdescribed above, some nano structures of the nano structures 20 in whichthe semiconductor layer 40 is formed confine light and are used as pathsof electrons and holes, and the remaining nano structures may be usedfor photoelectric conversion. For example, a half of the nano structures20 of in which the semiconductor layer 40 is formed may trap incidentlight and be used as pass of electrons and holes, and the remaining halfmay be used for converting light to power. Further, by using the resinlayer 30, the solar cell 100 having a structure that is shown in FIG. 1can be produced.

The resin layer 30 is positioned on the first conductive layer 10. Theresin layer 30 is filled at space between the plurality of nanostructures 20 to contact with the dielectric layer 22 that is positionedat a surface of the plurality of nano structures 20. Here, thedielectric layer 22 is formed at a surface of the plurality of nanostructures 20 and passivates the plurality of nano structures 20. Forthis purpose, the dielectric layer 22 is made of a material includingaluminum oxide (Al₂O₃), silicon nitride SiN_(x), silicon carbide (SiC),or silicon dioxide (SiO₂) having characteristics that prevent reflectionor having passivation characteristics. Particularly, aluminum oxide(Al₂O₃) is excellent in a passivation ability for a p-type semiconductormaterial, and silicon nitride (SiN_(x)) or silicon dioxide (SiO₂) isexcellent in a passivation ability for a p-type semiconductor material.The dielectric layer 22 prevents charges generated at a surface of thenano structures 20 from recombining, thereby well transferring holes orcharged that are generated in the nano structures 20 to the outsidewithout damage. As a result, by enhancing transfer efficiency ofelectrons or holes, an electromotive force of the solar cell 100 can beimproved. Meanwhile, at a surface in which the plurality of nanostructures 20 contact with the first semiconductor layer 402, thedielectric layer 22 is not formed for a semiconductor junction. In somecase, a production of the dielectric layer 22 may be omitted.

As shown in FIG. 1, the electron transfer body 24 is positioned on thefirst conductive layer 10 and contacts with a lower end portion of theplurality of nano structures 20. Here, the electron transfer body 24 ismade of metal. Therefore, electrons that are generated by an interactionwith the semiconductor layer 40 and the nano structures 20 efficientlyflow toward the first conductive layer 10 through the electron transferbody 24. For this purpose, the electron transfer body 24 may be made ofmetal such as nickel. That is, the electron transfer body 24 and thesecond conductive layer 50 may include the same metal.

Further, an average value of an average diameter of the electrontransfer body 24, i.e., a diameter of a section of the electron transferbody 24 that is taken in an xy-plane direction is larger than that of anaverage diameter of the plurality of nano structures 20, i.e., adiameter of a section of the nano structure 20 that is taken in anxy-plane direction. Therefore, electrons that are generated at theplurality of nano structures 20 efficiently escape toward the firstconductive layer 10 through the electron transfer body 24.

The semiconductor layer 40 includes a first semiconductor layer 402, asecond semiconductor layer 404, and a third semiconductor layer 406. Aplurality of semiconductor layers 402, 404, and 406 are shown in FIG. 1,but a semiconductor layer may be formed in one layer or two layers.Further, the number of semiconductor layers may be four or more.

Here, the semiconductor layer 40 may be formed at one time with a methodof changing only a doping source while injecting SiH₄ gas into a chamberby plasma enhanced chemical vapor deposition (PECVD). Because theplurality of nano structures 20 include a semiconductor material, theplurality of nano structures 20 form a semiconductor junction with thesemiconductor layer 40. For example, the nano structure 20 may be madeof an n+ type semiconductor material, the first semiconductor layer 402may be made of an n-type material, the second semiconductor layer 404may be made of an intrinsic material, and the third semiconductor layer406 may be made of a p-type semiconductor material. Here, the usedplurality of nano structures 20 and semiconductor layer 40 may be formedby ion doping silicon. In this case, because the plurality of nanostructures 20, the first semiconductor layer 402, the secondsemiconductor layer 404, and the third semiconductor layer 406 areconformally formed, by lowering an energy band gap, an electromotiveforce can be efficiently improved. Amorphous silicon is used as anintrinsic material. The plurality of nano structures 20 that are made ofan n+ type semiconductor material are used as a conduction passage ofelectrons and a selective emitter. Because the second conductive layer50 is positioned on the third semiconductor layer 406, the secondconductive layer 50 totally reflects light that transmits the thirdsemiconductor layer 406 and thus an electromotive force that isgenerated by the nano structures 20 and the semiconductor layer 40 canbe maximized.

Although not shown in FIG. 1, the nano structure 20 is made of an n-typesemiconductor material or an n+ type semiconductor material, asemiconductor layer that covers the nano structure 20 is formed in twolayers, a layer that contacts with the nano structure 20 is made of anintrinsic material, a layer that covers the above layer is made of ap-type semiconductor material. Further, the nano structure 20 may bemade of an n-type semiconductor material or an n+ type semiconductormaterial, and a semiconductor layer that covers the nano structure 20may be made of a p-type semiconductor material. The above-describedsemiconductor materials may be produced using amorphous silicon.

The cover layer 70 covers the second conductive layer 50 and contactswith a side surface of the resin layer 30. The cover layer 70 is made ofpolydimethylsiloxane (PDMS) or polyimide. Because the cover layer 70 ismade of such a material, the solar cell 100 has flexiblecharacteristics. Therefore, by grasping the cover layer 70 by a hand,the solar cell 100 may be bent.

As shown in FIG. 1, the contact electrodes 60 and 62 include a firstcontact electrode 60 and a second contact electrode 62. The firstcontact electrode 60 is positioned at the inside of the cover layer 70.The first contact electrode 60 contacts with the second conductive layer50 and electrically connects the second conductive layer 50 to theoutside. That is, the first contact electrode 60 connects the drawn-outwiring 80 and the second conductive layer 50. Hereinafter, a method ofmanufacturing the solar cell 100 of FIG. 1 will be described in detailwith reference to FIGS. 2 to 12.

FIG. 2 schematically shows a flowchart illustrating a process ofmanufacturing the solar cell 100 of FIG. 1, and FIGS. 3 to 12 illustrateeach step of a process of manufacturing the solar cell 100 of FIG. 2.Hereinafter, a process of manufacturing the solar cell 100 will besequentially described in detail with reference to FIGS. 2 and 3 to 12.

First, the substrate 29 and the plurality of nano structures 20 (shownin FIG. 3) are provided (S10). The substrate 29 and the plurality ofnano structures 20 are formed by doping silicon into an n+ type. Aproduction cost of the solar cell 100 (shown in FIG. 1) can be reducedusing the substrate 29 and a plurality of nano structures 20 that aremade of a relatively cheap material. Here, the substrate 29 and theplurality of nano structures 20 may be integrally provided byelectroless etching bulk silicon using a particle such as Ag. Further,in order to manufacture the plurality of nano structures 20 in a coneshape, the plurality of nano structures 20 may be additionally etchedusing a solution such as KOH.

Next, the dielectric layer 22 is provided on a surface of the pluralityof nano structures 20 (S20) (shown in FIG. 4). The dielectric layer 22may be deposited on a surface of the substrate 29 and the plurality ofnano structures 20.

The resin layer 30 contacting with the dielectric layer 22 is provided(S30) (shown in FIG. 5). The resin layer 30 is formed on the substrate29. The resin layer 30 is filled at space between the plurality of nanostructures 20 and contacts with the dielectric layer 22. For example,liquid resin is disposed at space between the plurality of nanostructures 20 to be spin coated, and then is cured, thereby forming theresin layer 30.

Next, by etching an upper portion of the resin layer 30 and thedielectric layer 22, the plurality of nano structures 20 are partiallyexposed (S40) (shown in FIG. 6). Here, the dielectric layer 22 is aportion contacting with an upper part of the resin layer 30. Therefore,an upper portion of the plurality of nano structures 20 is exposed tothe outside on the resin layer 30.

The semiconductor layer 40 is formed on the plurality of nano structures20 (S50). Here, the semiconductor layer 40 includes a plurality of firstsemiconductor portions 40 a and a second semiconductor portion 40 b. Theplurality of first semiconductor portions 40 a are positioned on theplurality of first nano structures 20. A width W between upper endportions 401 a of the plurality of first semiconductor portions 40 a maybe 100 nm to 2 μm. If the width W between upper end portions 401 a ofthe plurality of first semiconductor portions 40 a is so small, theplurality of first nano structures 20 are so densely formed and thus itis difficult to form the resin layer 30 at space therebetween. Incontrast, if the width W between upper end portions 401 a of theplurality of first semiconductor portions 40 a is too large, theplurality of first nano structures 20 are so sparcely formed and thus itis difficult to obtain a desired light electromotive force. If the widthW between the upper end portions 401 a of the plurality of firstsemiconductor portions 40 a is small, it is advantageous to trap light.If the width W between the upper end portions 401 a of the plurality offirst semiconductor portions 40 a is large, a contact area of the firstsemiconductor portions 40 a and the nano structure 20 is enlarged andthus it is advantageous for carrier collection. The second semiconductorportion 40 b is connected to and integrally formed with the plurality offirst semiconductor portions 40 a and is positioned on the firstconductive layer 30.

Next, the conductive layer 50 is provided on the semiconductor layer 40(S60) (shown in FIG. 8). The semiconductor layer 40 includes a firstsemiconductor layer 402, a second semiconductor layer 404, and a thirdsemiconductor layer 406 that are sequentially stacked through multi-stepdeposition and doping. As shown in FIG. 8, a thickness t50 of theconductive layer 50 may be 20 μm to 100 μm. The thickness t50 of theconductive layer 50 may be changed according to a length of the nanostructure 20. If the thickness t50 of the conductive layer 50 is solarge, a thickness of the solar cell 100 may increase. In contrast, ifthe thickness t50 of the conductive layer 50 is so small, thesemiconductor layer 40 may be exposed to the outside, and thus lightreflection by the conductive layer 50 is difficult. As a result,generation of an electromotive force of the solar cell 100 isdeteriorated. In order not to transmit light of a long wavelength or forhanding, it is necessary that the conductive layer 50 has somewhat athickness. The conductive layer 50 is formed by performing electrolessplating on the conductive layer 50.

As shown in FIG. 9, the contact electrode 60 is formed on the conductivelayer 50. For example, after the contact electrode 60 is deposited onthe conductive layer 50, the drawn-out wiring 80 is connected to thecontact electrode 60. Therefore, power that is transmitted through theconductive layer 50 may be supplied to the outside through the contactelectrode 60 and the drawn-out wiring 80.

The cover layer 70 for covering the conductive layer 50 is provided(S70) (shown in FIG. 10). The cover layer 70 is formed by covering theresin layer 30, the conductive layer 50, and the contact electrode 60 onthe substrate 29. Therefore, an external appearance of the solar cell100 (shown in FIG. 1) is formed using the cover layer 70. The coverlayer 70 is formed by spin coating and curing a resin.

Next, the substrate 29 is separated from the resin layer 30 in an arrowdirection (S80) (shown in FIG. 11). The separated substrate 29 formsanother solar cell by recycling.

A hole 301 is formed in the resin layer 30 (S90) (shown in FIG. 11).That is, by etching the resin layer 30 corresponding to a lower endportion of the nano structures 20 with potassium hydroxide KOH, the hole301 is formed.

The electron transfer body 24 is provided to the hole 301 (S100) (shownin FIG. 12). The electron transfer body 24 may be provided by covering amask in a lower part of the resin layer 30, exposing only the hole 301,and performing electroless plating.

Next, another conductive layer 10 is provided under the resin layer 30(S110) (shown in FIG. 12). Here, a light transmittance of the otherconductive layer 10 is lower than that of the conductive layer 50. Athickness t10 of the other conductive layer 10 may be 500 nm to 10 μm.If the thickness t10 of the conductive layer 10 is so large, a lighttransmittance of the conductive layer 10 may be deteriorated. Here, itis preferable that a light transmittance is maintained to 80% or more.Further, if the thickness t10 of the conductive layer 10 is so small,the conductive layer 10 has a very small thickness and thus anelectrical connection state to the outside is not good. Furthermore, ifthe thickness t10 of the conductive layer 10 is so small, illuminance ofthe conductive layer 10 is smaller than that of a surface of the nanostructure 20 and thus the conductive layer 10 cannot fully cover thenano structure 20. Therefore, the conductive layer 10 having a thicknesst10 of the above-described range is formed.

FIG. 13 schematically shows a cross-sectional view of a solar cell 200according to a second exemplary embodiment of the present invention. Thestructure of the solar cell 200 of FIG. 13 is similar to that of thesolar cell 100 of FIG. 1, except for the dielectric layer 22 and theresin layer 30 of FIG. 1, and thus the same elements as those of FIG. 1are denoted by the same reference numerals and a detailed descriptionthereof will be omitted. Further, the structure of the solar cell 200 ofFIG. 13 only illustrates the present invention and the present inventionis not limited thereto. Therefore, the section structure of the solarcell 200 may be changed to other forms.

As shown in FIG. 13, an electron transfer body 21 covers a firstconductive layer 10. Here, the electron transfer body 21 contacts with afirst semiconductor layer 402. The electron transfer body 21 includes ap+ type semiconductor material or an n+ type semiconductor material.When the electron transfer body 21 is a p+ type semiconductor material,for example, p+ type doped silicon, nano structures 20, the firstsemiconductor layer 402, a second semiconductor layer 404, and a thirdsemiconductor layer 406 may be made of a p-type semiconductor material,an intrinsic material, an n-type semiconductor material, and an n+ typesemiconductor material, respectively. Therefore, by conformally formingthe plurality of nano structures 20 and the semiconductor layer 40, anenergy band gap can be lowered. In FIG. 13, three semiconductor layers402, 404, and 406 are included, but one, two, or four or moresemiconductor layers may be formed.

FIG. 14 schematically shows a flowchart illustrating a manufacturingprocess of the solar cell 200 of FIG. 13, and FIGS. 15 to 20 illustrateeach step of a manufacturing process of the solar cell 200 of FIG. 14.Hereinafter, a manufacturing process of the solar cell 200 will besequentially described with reference to FIGS. 14 and 15 to 20.

First, a substrate 29 and a plurality of nano structures 20 (shown inFIG. 15) are provided (S12). The substrate 29 and the plurality of nanostructures 20 are produced by doping silicon into an n+ type. Thesubstrate 29 and the plurality of nano structures 20 are produced byelectroless etching bulk silicon using a particle such as Ag. Further,in order to form the plurality of nano structures 20 in a cone shape,the plurality of nano structures 20 may be additionally etched by KOH.

At least one semiconductor layer 40 is provided on the plurality of nanostructures 20 (S22). That is, as shown in FIG. 16, three semiconductorlayers 402, 404, and 406 may be formed. The semiconductor layer 40 maybe formed by ion doping.

Next, the conductive layer 50 is provided on the semiconductor layer 40(S32) (shown in FIG. 17). Further, a contact electrode 60 forelectrically connecting the conductive layer 50 to the outside isprovided on the conductive layer 50. For example, after the contactelectrode 60 is deposited on the conductive layer 50, a drawn-out wiring80 is connected to the contact electrode 60. Therefore, power that istransmitted through the conductive layer 50 is supplied to the outsidethrough the contact electrode 60 and the drawn-out wiring 80.

A cover layer 70 for covering the conductive layer 50 is provided (S42)(shown in FIG. 18). The cover layer 70 is formed by covering theconductive layer 50 and the contact electrode 60 on the substrate 29.Therefore, an external appearance of the solar cell 200 is formed usingthe cover layer 70 (shown in FIG. 13).

Next, the substrate 29 is separated from the semiconductor layer 40 inan arrow direction (S52) (shown in FIG. 19). By recycling the separatedsubstrate 29, another solar cell can be produced.

As shown in an enlarged circle of FIG. 19, a lower surface 20 s of thenano structure 20 in which the substrate 29 is removed is unevenlyformed. Therefore, light that is applied through the lower surface 20 sis not reflected by the lower surface 20 s and is well applied to thenano structure 20. Therefore, optical absorption efficiency of the nanostructure 20 can be maximized. The lower surface 20 s of the nanostructure 20 may be irregularly formed by grinding, as needed.

Another semiconductor layer 21 is provided under the plurality of nanostructures 20 (S62) (see FIG. 20). Here, the other semiconductor layer21 is made of an n+ type semiconductor material or a p+ typesemiconductor material. Another semiconductor layer 21 is formed by iondoping. The lower surface 20 s (shown in FIG. 19) of the nano structure20 contacts with another semiconductor layer 21. Because anothersemiconductor layer 21 is made of the foregoing semiconductor material,light reflection may be large. However, because the lower surface 20 sof the nano structure 20 is unevenly formed, light reflection can beprevented to the maximum.

Next, another conductive layer 10 is provided under anothersemiconductor layer 21 (S72) (shown in FIG. 20). Here, in a visible rayarea, a light transmittance of the other conductive layer 10 is lowerthan that of the conductive layer 50.

FIG. 21 schematically shows a section structure of a solar cell 300according to a third exemplary embodiment of the present invention. Thestructure of the solar cell 300 of FIG. 21 is similar to that of thesolar cell 200 of FIG. 13, and thus the same elements as those of FIG.13 are denoted by the same reference numerals and a detailed descriptionthereof will be omitted. Further, a structure of the solar cell 300 ofFIG. 21 only illustrates the present invention, and the presentinvention is not limited thereto. Therefore, a section structure of thesolar cell 300 may be changed to other forms.

As shown in FIG. 21, the first conductive layer 10 directly contactswith a plurality of semiconductor layers 40 and the plurality of nanostructures 20. Here, the plurality of nano structures 20, a firstsemiconductor layer 402, a second semiconductor layer 404, and a thirdsemiconductor layer 406 are made of a p+ type semiconductor material, ap-type semiconductor material, an intrinsic material, and an n-typesemiconductor material, respectively. Alternatively, the plurality ofnano structures 20, the first semiconductor layer 402, the secondsemiconductor layer 404, and the third semiconductor layer 406 may bemade of an n+ type semiconductor material, an n-type semiconductormaterial, an intrinsic material, and a p-type semiconductor material,respectively. Therefore, by lowering an energy band gap through theconformally formed first conductive layer 10, plurality of semiconductorlayers 40, and plurality of nano structures 20, photoelectric conversionefficiency of the solar cell 300 can be maximized.

FIG. 22 schematically shows a cross-sectional view of a solar cell 400according to a fourth exemplary embodiment of the present invention. Thestructure of the solar cell 400 of FIG. 22 is similar to that of thesolar cell 300 of FIG. 21, and thus the same elements as those of FIG.21 are denoted by the same reference numerals and a detailed descriptionthereof will be omitted. Further, the structure of the solar cell 400 ofFIG. 22 only illustrates the present invention and the present inventionis not limited thereto. Therefore, the cross-sectional view of the solarcell 400 may be changed to other forms.

As shown in FIG. 22, an anti-reflection (AR) layer 64 is provided underanother conductive layer 10. By enabling light to be not reflected, theAR layer 64 absorbs light that is applied to the solar cell 400 to themaximum. As a result, light absorption efficiency of the solar cell 400can be maximized.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

DESCRIPTION OF SYMBOLS

100, 200, 300. solar cell 10, 50. conductive layer 101, 291. platesurface 20. nano structure 20s. lower surface 22. dielectric layer 24.electron transfer body 29. substrate 30. resin layer 301. hole 21, 40,402, 404, 406. semiconductor layer 40a, 40b. semiconductor portion 401a.upper end portion 60, 62. contact electrode 64. anti-reflection layer70. cover layer 80. drawn-out wiring P. passive element

What is claimed is:
 1. A solar cell, comprising: a first conductivelayer; a plurality of nano structures that are positioned on the firstconductive layer and that are extended to cross a surface of the firstconductive layer and that are separated from each other; a resin layerthat is positioned on the first conductive layer and that is filledat-in-a space between the plurality of nano structures; at least onesemiconductor layer that is positioned on the resin layer and thatcovers the plurality of nano structures; a second conductive layer thatcovers the semiconductor layer and that has a light transmittance lowerthan that of the first conductive layer; and at least one electrontransfer body that is positioned on the first conductive layer and thatcontacts with a lower end portion of the plurality of nano structures,wherein the electron transfer body covers the first conductive layer,and the electron transfer body comprises a p+ type semiconductormaterial or an n+ type semiconductor material.
 2. The solar cell ofclaim 1 further comprising a dielectric layer that is positioned on asurface of the plurality of nano structures and that contacts with theresin layer.
 3. The solar cell of claim 1, wherein the second conductivelayer has a thickness of 20 μm to 100 μm.
 4. The solar cell of claim 1,wherein the second conductive layer and the electron transfer bodycomprise the same metal.
 5. The solar cell of claim 4, wherein the metalis at least one element that is selected from a group consisting ofaluminum (Al), silver (Ag), nickel (Ni), gold (Au), and platinum (Pt).6. The solar cell of claim 1, wherein the at least one semiconductorlayer comprises a plurality of semiconductor layers, and a semiconductorlayer contacting with the electron transfer body of the plurality ofsemiconductor layers comprises an intrinsic material.
 7. The solar cellof claim 1, wherein the at least one semiconductor layer comprises aplurality of semiconductor layers, and at least one semiconductor layerof the plurality of semiconductor layers comprises a plurality of firstsemiconductor portions that are positioned on the plurality of firstnano structures; and a second semiconductor portion that is connected tothe first semiconductor portion to be integrally formed with the firstsemiconductor portion and that is positioned on the resin layer, whereina width between upper end portions of the plurality of firstsemiconductor portions is 100 nm to 2 μm.
 8. The solar cell of claim 1further comprising a cover layer that covers the second conductive layerand that contacts with a side surface of the resin layer.
 9. The solarcell of claim 8 further comprising a contact electrode that ispositioned within the cover layer and that electrically connects thesecond conductive layer to the outside by contacting with the secondconductive layer.
 10. The solar cell of claim 1, wherein the pluralityof nano structures comprise a semiconductor material.
 11. The solar cellof claim 1, wherein the first conductive layer has a thickness of 30 nmto 300 nm.
 12. The solar cell of claim 1, wherein the dielectric layercomprises at least one material that is selected from a group consistingof aluminum oxide (Al₂O₃), silicon nitride (SiN_(x)), silicon carbide(SiC), and silicon dioxide (SiO_(x)).